ESAT 2016: 83 questions decoded out of 85, by method and by chapter.

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The paper at a glance, coloured by move. Click a square to open its question; empty squares are not decoded yet.

• 55Natural selection edits pre-existing random variation, the environment never writes itKey methodBiologyInheritance, Variation & Evolution4 other sittings

  Same method, other sittings

  2018202020212022

  Worked solutionOpen the method
• 56Osmosis moves water toward the more concentrated solutionPavlovBiologyMembrane Transport, Cell Division & Reproduction6 other sittings

  Same method, other sittings

  201720182020202120222023

  Worked solutionOpen the method
• 57Prokaryote versus eukaryote: the defining feature contrast (wall, nucleus, mitochondria, chloroplasts)PavlovBiologyCells5 other sittings

  Same method, other sittings

  20172019202020212023

  Worked solutionOpen the method
• 58Denaturation is loss of the active-site shape, caused by heat, extreme pH or boilingBiology arithmetic reflexes: percentage over the original, rate as amount over time, area as radius squaredAn enzyme is a protein catalyst, not a living thing: eliminate options that contradict its natureKey methodBiologyEnzymes5 other sittings

  Same method, other sittings

  20192020202120222023

  Worked solutionOpen the method

  AlsoBiology arithmetic reflexes: percentage over the original, rate as amount over time, area as radius squaredAn enzyme is a protein catalyst, not a living thing: eliminate options that contradict its nature
• 59Counting alleles across a pedigree: body cells are diploid, mind the sex chromosomesTunnelBiologyInheritance, Variation & Evolution2 other sittings

  Same method, other sittings

  20192023

  Worked solutionOpen the method
• 60Denaturation is loss of the active-site shape, caused by heat, extreme pH or boilingRate follows collision frequency and concentration, not the total amountKey methodBiologyEnzymes3 other sittings

  Same method, other sittings

  201920222023

  Worked solutionOpen the method

  AlsoRate follows collision frequency and concentration, not the total amount
• 61Plateaux and the compensation point: a level rate means another factor limits, a falling rate means denaturationVolume in a capillary tube is a cylinder: pi times radius squared times length, radius is half the diameterKey methodBiologyEcology & Plant Physiology4 other sittings

  Same method, other sittings

  2018202020222023

  Worked solutionOpen the method

  AlsoVolume in a capillary tube is a cylinder: pi times radius squared times length, radius is half the diameter
• 62What a light microscope actually resolves, and when chromosomes are visiblePavlovBiologyCellsonly this sitting

  Same method, other sittings

  This one has only struck here so far.

  Worked solutionOpen the method
• 63Trace the auxin: shoots bend to light, roots to gravity, driven by uneven hormone from an intact tipPavlovBiologyEcology & Plant Physiology2 other sittings

  Same method, other sittings

  20172018

  Worked solutionOpen the method
• 64DNA base arithmetic: pairing rules bind the whole molecule, never a single strandKey methodBiologyDNA, Protein Synthesis & Gene Technology3 other sittings

  Same method, other sittings

  201820202021

  Worked solutionOpen the method
• 65Monohybrid cross Aa x Aa gives a 1:2:1 genotype ratio and a 3:1 phenotype ratioProbability of a specific sex and a specific genotype: multiply the two independent chancesTunnelBiologyInheritance, Variation & Evolution5 other sittings

  Same method, other sittings

  20172018202120222023

  Worked solutionOpen the method

  AlsoProbability of a specific sex and a specific genotype: multiply the two independent chances
• 66Classify the interaction: same species or different, and who benefitsPavlovBiologyEcology & Plant Physiology1 other sitting

  Same method, other sittings

  2023

  Worked solutionOpen the method
• 67Mitosis keeps the chromosome number and makes two cells, meiosis halves it and makes fourSeparate chromosome, DNA molecule and strand, and watch for the replication doublingKey methodBiologyMembrane Transport, Cell Division & Reproduction6 other sittings

  Same method, other sittings

  201720182020202120222023

  Worked solutionOpen the method

  AlsoSeparate chromosome, DNA molecule and strand, and watch for the replication doubling
• 68Read a tissue or organ from the difference between blood entering and leaving itRespiration signature in blood; hard exercise adds lactate and lowers pHKey methodBiologyAnimal Physiology: Systems, Homeostasis & Disease2 other sittings

  Same method, other sittings

  20202021

  Worked solutionOpen the method

  AlsoRespiration signature in blood; hard exercise adds lactate and lowers pH
• 69Counting alleles across a pedigree: body cells are diploid, mind the sex chromosomesTunnelBiologyInheritance, Variation & Evolution2 other sittings

  Same method, other sittings

  20192023

  Worked solutionOpen the method
• 70Oxygen sag below organic pollution: bacteria strip the oxygen, and indicator species track the curveKey methodBiologyEcology & Plant Physiology3 other sittings

  Same method, other sittings

  201720182020

  Worked solutionOpen the method
• 71A rise-then-plateau curve means a factor is now limiting; plateau height is set by total substrateKey methodBiologyEnzymes4 other sittings

  Same method, other sittings

  2019202020212022

  Worked solutionOpen the method
• 72Read a coding strand in non-overlapping triplets from the left and translate with the tableSubstitution hits one codon; an insertion or deletion reframes everything downstreamTunnelBiologyDNA, Protein Synthesis & Gene Technology2 other sittings

  Same method, other sittings

  20172019

  Worked solutionOpen the method

  AlsoSubstitution hits one codon; an insertion or deletion reframes everything downstream

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The paper at a glance, coloured by move. Click a square to open its question; empty squares are not decoded yet.

• 37Read a nuclide symbol into protons, neutrons and electronsPavlovChemistryAtomic Structure, Bonding & the Periodic Table5 other sittings

  Same method, other sittings

  20172018201920212023

  Worked solutionOpen the method
• 38Electron accounting: turn charge into moles, then read every amount off the half-equationsMolten electrolysis always splits the compound into its two elementsTunnelChemistryElectrolysis & Metals4 other sittings

  Same method, other sittings

  2017201920202021

  Worked solutionOpen the method

  AlsoMolten electrolysis always splits the compound into its two elements
• 39Classify the structure and bonding, then read off the propertyKey methodChemistryAtomic Structure, Bonding & the Periodic Table6 other sittings

  Same method, other sittings

  201820192020202120222023

  Worked solutionOpen the method
• 40Screen an equilibrium with the three Le Chatelier leversKey methodChemistryRates of Reaction & Energetics2 other sittings

  Same method, other sittings

  20172018

  Worked solutionOpen the method
• 41Empirical formula: masses to moles to the simplest whole number ratioTunnelChemistryQuantitative Chemistry3 other sittings

  Same method, other sittings

  201720192022

  Worked solutionOpen the method
• 42Bound the relative atomic mass between the isotope masses to eliminate optionsBack out the element from a given electron count, undoing the ionic charge firstKey methodChemistryAtomic Structure, Bonding & the Periodic Table5 other sittings

  Same method, other sittings

  20172018202020222023

  Worked solutionOpen the method

  AlsoBack out the element from a given electron count, undoing the ionic charge first
• 43Rf equals spot distance over solvent-front distanceInterpreting a chromatogram: purity, identity, mobility and phasesPavlovChemistryOrganic Chemistry, Separation & Analysis6 other sittings

  Same method, other sittings

  201720182019202020212022

  Worked solutionOpen the method

  AlsoInterpreting a chromatogram: purity, identity, mobility and phases
• 44Read a rate-time curve as two separate things: plateau and steepnessKey methodChemistryRates of Reaction & Energetics4 other sittings

  Same method, other sittings

  2017201920202022

  Worked solutionOpen the method
• 45Judge a reaction as redox from its type before assigning oxidation numbersElectron direction in a half-equation: left means reduction, right means oxidationKey methodChemistryChemical Reactions, Acids, Bases & Redox5 other sittings

  Same method, other sittings

  20172018201920222023

  Worked solutionOpen the method

  AlsoElectron direction in a half-equation: left means reduction, right means oxidation
• 46Name an unknown product from the atoms left over after the known productsKey methodChemistryChemical Reactions, Acids, Bases & Redox2 other sittings

  Same method, other sittings

  20212022

  Worked solutionOpen the method
• 47Aqueous electrolysis discharge rules: below hydrogen deposits, halide gives the halogenElectron accounting: turn charge into moles, then read every amount off the half-equationsIn amount MCQs the wrong options are the electron-count and diatomic-gas slipsKey methodChemistryElectrolysis & Metals6 other sittings

  Same method, other sittings

  201720182019202020212022

  Worked solutionOpen the method

  AlsoElectron accounting: turn charge into moles, then read every amount off the half-equationsIn amount MCQs the wrong options are the electron-count and diatomic-gas slips
• 48Reverse activation energy is the forward barrier plus the heat releasedPavlovChemistryRates of Reaction & Energeticsonly this sitting

  Same method, other sittings

  This one has only struck here so far.

  Worked solutionOpen the method
• 49Strong versus weak acid: only the hydrogen ion properties differ, not the amount of acidKey methodChemistryChemical Reactions, Acids, Bases & Redox2 other sittings

  Same method, other sittings

  20172023

  Worked solutionOpen the method
• 50Mass by difference: the component asked for is the leftover, and its molar mass is often a decoyPin exactly what is asked: the examiner plants the natural intermediate value as an optionKey methodChemistryQuantitative Chemistry4 other sittings

  Same method, other sittings

  2018202020212022

  Worked solutionOpen the method

  AlsoPin exactly what is asked: the examiner plants the natural intermediate value as an option
• 51Ion charges fix the formula, the reacting ratio and the number of ionsMolar gas volume both ways, and the two traps: cubic decimetres versus cubic centimetres, and diatomic gasesPavlovChemistryQuantitative Chemistry3 other sittings

  Same method, other sittings

  201820212023

  Worked solutionOpen the method

  AlsoMolar gas volume both ways, and the two traps: cubic decimetres versus cubic centimetres, and diatomic gases
• 52Diprotic acid reflex: sulfuric and ethanedioic acid react two to one with a monobasic basePavlovChemistryQuantitative Chemistry2 other sittings

  Same method, other sittings

  20202021

  Worked solutionOpen the method
• 53Electron accounting: turn charge into moles, then read every amount off the half-equationsTrack the bulk solution, not just the electrodes: concentration and pH changesTunnelChemistryElectrolysis & Metals6 other sittings

  Same method, other sittings

  201720182019202020212023

  Worked solutionOpen the method

  AlsoTrack the bulk solution, not just the electrodes: concentration and pH changes
• 54Bond-energy balance: broken minus formed, counting every bondExploit the bond-energy option list: sign, factor and phantom bondsTunnelChemistryRates of Reaction & Energetics4 other sittings

  Same method, other sittings

  2017201920212023

  Worked solutionOpen the method

  AlsoExploit the bond-energy option list: sign, factor and phantom bonds

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The paper at a glance, coloured by move. Click a square to open its question; empty squares are not decoded yet.

• 1Rearranging Complex FormulasPavlovPureAlgebra, Functions & Graphs4 other sittings

  Same method, other sittings

  2019202120222023

  Worked solutionOpen the method
• 3Chaining ratios by scaling the common termPavlovPureRatio & Proportion2 other sittings

  Same method, other sittings

  20192020

  Worked solutionOpen the method
• 4Convert means into absolute totalsPavlovProb & StatsProbability & Statistics4 other sittings

  Same method, other sittings

  2018202020222023

  Worked solutionOpen the method
• 5Successive percentage changes as a product of decimal multipliersPavlovPureRatio & Proportion5 other sittings

  Same method, other sittings

  20182019202020212022

  Worked solutionOpen the method
• 6Bearings: use back-bearings and subtraction to find anglesPavlovPureGeometry3 other sittings

  Same method, other sittings

  201720182019

  Worked solutionOpen the method
• 7Setting up the proportionality constantTunnelPureRatio & Proportion5 other sittings

  Same method, other sittings

  20172018202020222023

  Worked solutionOpen the method
• 8The solving for x multiple-choice trapKey methodPureGeometry2 other sittings

  Same method, other sittings

  20192022

  Worked solutionOpen the method
• 9Rearranging Complex FormulasPavlovPureAlgebra, Functions & Graphs4 other sittings

  Same method, other sittings

  2019202120222023

  Worked solutionOpen the method
• 11Algebraic Fraction SimplificationPavlovPureAlgebra, Functions & Graphs6 other sittings

  Same method, other sittings

  201720192020202120222023

  Worked solutionOpen the method
• 12Fill the two-way table for overlapping categoriesTunnelProb & StatsProbability & Statistics2 other sittings

  Same method, other sittings

  20172018

  Worked solutionOpen the method
• 13Reduce exponential equations to a single prime basePavlovPureNumber & Units3 other sittings

  Same method, other sittings

  201720192023

  Worked solutionOpen the method
• 14Regular polygons: work with exterior angles, not interiorPavlovPureGeometry3 other sittings

  Same method, other sittings

  201720182022

  Worked solutionOpen the method
• 15Set up algebraic probability treesTunnelProb & StatsProbability & Statistics4 other sittings

  Same method, other sittings

  2017201920212023

  Worked solutionOpen the method
• 16System to Single QuadraticPavlovPureAlgebra, Functions & Graphs2 other sittings

  Same method, other sittings

  20182021

  Worked solutionOpen the method
• 17Rhombus area from diagonalsPavlovPureGeometry1 other sitting

  Same method, other sittings

  2019

  Worked solutionOpen the method
• 18Polynomial InequalitiesTunnelPureCoordinate Geometry2 other sittings

  Same method, other sittings

  20172019

  Worked solutionOpen the method

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The paper at a glance, coloured by move. Click a square to open its question; empty squares are not decoded yet.

• 47Quadratics in DisguiseKey methodPureAlgebra, Functions & Graphs3 other sittings

  Same method, other sittings

  202020212022

  Worked solutionOpen the method
• 49Geometric OptimisationTunnelPureDifferentiation2 other sittings

  Same method, other sittings

  20182021

  Worked solutionOpen the method
• 51Integrate With Respect to yKey methodPureIntegrationonly this sitting

  Same method, other sittings

  This one has only struck here so far.

  Worked solutionOpen the method
• 53Graphing to Count RootsTunnelPureDifferentiationonly this sitting

  Same method, other sittings

  This one has only struck here so far.

  Worked solutionOpen the method

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The paper at a glance, coloured by move. Click a square to open its question; empty squares are not decoded yet.

• 73Factor and Remainder TheoremPavlovPureAlgebra, Functions & Graphs3 other sittings

  Same method, other sittings

  201720202023

  Worked solutionOpen the method
• 75Circle equation signs: expanded coefficients have opposite signs to the centrePavlovPureCoordinate Geometryonly this sitting

  Same method, other sittings

  This one has only struck here so far.

  Worked solutionOpen the method
• 77Discarding the Extraneous RootKey methodPureSequences & Series3 other sittings

  Same method, other sittings

  201820202023

  Worked solutionOpen the method
• 79Shaded areas by structural subtractionPavlovPureGeometry2 other sittings

  Same method, other sittings

  20192020

  Worked solutionOpen the method
• 81Pythagorean Substitution to QuadraticKey methodPureTrigonometry2 other sittings

  Same method, other sittings

  20192020

  Worked solutionOpen the method
• 83Roots via the DiscriminantKey methodPureAlgebra, Functions & Graphs2 other sittings

  Same method, other sittings

  20182022

  Worked solutionOpen the method
• 85Perpendicular lines: the product of their gradients is -1PavlovPureCoordinate Geometry2 other sittings

  Same method, other sittings

  20172021

  Worked solutionOpen the method
• 87Quadratic Derivative ConditionsPavlovPureDifferentiation1 other sitting

  Same method, other sittings

  2020

  Worked solutionOpen the method
• 89Sequential Curve TransformationsTunnelPureAlgebra, Functions & Graphs1 other sitting

  Same method, other sittings

  2017

  Worked solutionOpen the method

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The paper at a glance, coloured by move. Click a square to open its question; empty squares are not decoded yet.

• 19In a vacuum every electromagnetic wave shares one speed, so frequency and wavelength are strictly inversePavlovPhysicsWaves, Sound & the Electromagnetic Spectrum2 other sittings

  Same method, other sittings

  20192021

  Worked solutionOpen the method
• 20Alpha and beta decay bookkeeping: fix the alpha count from the mass number firstTunnelPhysicsRadioactivity5 other sittings

  Same method, other sittings

  20172018201920202023

  Worked solutionOpen the method
• 21Heat transfer is driven by the temperature difference alone, never by the individual temperaturesConduction along a bar: rate is proportional to area times temperature difference, divided by lengthScale by the exponents: multiply the factor changes, never recompute the quantityKey methodPhysicsThermal Physics3 other sittings

  Same method, other sittings

  201820192022

  Worked solutionOpen the method

  AlsoConduction along a bar: rate is proportional to area times temperature difference, divided by lengthScale by the exponents: multiply the factor changes, never recompute the quantity
• 22Compound option tables: settle the cheapest quantity first and strike outKey methodPhysicsEnergy, Work & Momentum2 other sittings

  Same method, other sittings

  20172019

  Worked solutionOpen the method
• 23Nuclear reactions: balance nucleon number and proton number across the arrowTunnelPhysicsRadioactivity2 other sittings

  Same method, other sittings

  20172018

  Worked solutionOpen the method
• 24In a two state question, lock the invariant from state one before touching state twoChoose the power formula by the shared quantity, then split power as R or as one over RKey methodPhysicsElectricity & Magnetism6 other sittings

  Same method, other sittings

  201720182020202120222023

  Worked solutionOpen the method

  AlsoChoose the power formula by the shared quantity, then split power as R or as one over R
• 25A closed ideal switch is a plain wire: redraw before you computePavlovPhysicsElectricity & Magnetism3 other sittings

  Same method, other sittings

  202020212023

  Worked solutionOpen the method
• 26Scale by the exponents: multiply the factor changes, never recompute the quantityKey methodPhysicsThermal Physics1 other sitting

  Same method, other sittings

  2019

  Worked solutionOpen the method
• 27Total path of an oscillating particle is four times the amplitude per cycleKey methodPhysicsWaves, Sound & the Electromagnetic Spectrum3 other sittings

  Same method, other sittings

  201820192023

  Worked solutionOpen the method
• 28Free body first: list every force with its sign, then set the resultant equal to maChoose the system: the whole assembly for the acceleration, one body for an internal forceTunnelPhysicsKinematics & Forces4 other sittings

  Same method, other sittings

  2018202020212023

  Worked solutionOpen the method

  AlsoChoose the system: the whole assembly for the acceleration, one body for an internal force
• 29Find the current first: it is the hub of every electrical chainPavlovPhysicsElectricity & Magnetism4 other sittings

  Same method, other sittings

  2017202120222023

  Worked solutionOpen the method
• 30Let the option list choose your units, and kill options by dimensionsTurn what you are given into a mass before you divide by a volumePrism with a hole: subtract in the cross-section, multiply by the length onceKey methodPhysicsMatter6 other sittings

  Same method, other sittings

  201720182019202020212023

  Worked solutionOpen the method

  AlsoTurn what you are given into a mass before you divide by a volumePrism with a hole: subtract in the cross-section, multiply by the length once
• 31Heat transfer is driven by the temperature difference alone, never by the individual temperaturesSort the three transfer modes by what each one actually requiresKey methodPhysicsThermal Physics5 other sittings

  Same method, other sittings

  20172018201920202022

  Worked solutionOpen the method

  AlsoSort the three transfer modes by what each one actually requires
• 32Read a motion graph by gradient and area, one phase at a timeDistance, displacement and average speed are three different readings of the same motionTunnelPhysicsKinematics & Forces5 other sittings

  Same method, other sittings

  20172018201920202023

  Worked solutionOpen the method

  AlsoDistance, displacement and average speed are three different readings of the same motion
• 33Decay conserves atoms one for one: daughter equals initial daughter plus parent decayedKey methodPhysicsRadioactivity4 other sittings

  Same method, other sittings

  2017201920212022

  Worked solutionOpen the method
• 34When only a ratio is asked, form the ratio and let the unknowns cancelKey methodPhysicsMatter3 other sittings

  Same method, other sittings

  201720202021

  Worked solutionOpen the method
• 35The bridge between momentum and kinetic energyKey methodPhysicsEnergy, Work & Momentum2 other sittings

  Same method, other sittings

  20182019

  Worked solutionOpen the method
• 36Turn measured times into distances with the right geometric factor for reflected or multi-speed signalsKey methodPhysicsWaves, Sound & the Electromagnetic Spectrum3 other sittings

  Same method, other sittings

  201720212022

  Worked solutionOpen the method